Gas turbine engines generally comprise a compressor for compressing air for the support of combustion, a combustion chamber having inlets for the compressed air and a fuel, and a rotatable turbine for extracting energy from the combustion gases produced in the combustion chamber. The hot gases produced in the combustion chamber are fed to the turbine which produces mechanical energy at a drive shaft. Since all of the heat energy in the exhaust gases is not generally extractable by the turbine, efficiency is improved by providing a recuperative heat exchanger on the exhaust side of the turbine for preheating the compressed combustion air. The exhaust gas generally flows in cross or counter-current relation to the compressed air flowing through the heat exchanger.
One problem that must be faced in the use of a recuperative heat exchanger is that gas turbines often exhibit operating temperatures over 1,000.degree. C. The efficiency of the gas turbine depends in part on the efficiency of the heat exchanger in extracting the residual energy contained in the hot exhaust gases and preheating the compressed air supplied to the turbine. Because of the high temperature on the hot gas side of the heat exchanger, the materials for such equipment must be limited to highly heat resistant metals or ceramic materials. Moreover, since the efficiency of the heat exchanger is the ratio of heat actually transferred therein to the heat theoretically transferable by an infinitely large heat exchange surface, extensive heat exchange surface areas are required for recuperative heat exchanger of high efficiency.
Tube-type heat exchangers heretofore known and used require a great deal of the space. Thus, wherein weight and space are critical, such heat exchangers are impractical.
Cross flow heat exchangers of plate construction are also known as disclosed in "Problems of the Heat Exchanger for Vehicular Gas Turbines" by E. Tiefenbacher, in ASME Publication 76-GT-105 of 1976. However, substantial problems often arise relating to the control of heat stress to which the heat exchanger matrices are subject. It is also known to equip a gas turbines with a heat exchanger that operates regeneratively. Heat exchangers of this type often comprise ceramic discs that are driven in rotation. The discs revolve successively between segments of the exhaust and combustion air conduits so that there is alternately a heating and cooling of the discs in the respective heating and cooling zones. However, sealing of the rotating heat exchanger discs presents a serious problem because of the substantial pressure differential between the heating and cooling zones and because of the high environmental temperatures.
Thus, there is a need for an improved recuperative heat exchanger with a large heat exchange surface that can be packaged in a relatively compact assembly.